High-melting point components, such as metals and ceramics, can be built using additive manufacturing (AM) using one of two methods: powder bed fusion (PBF) or directed energy deposition (DED). In the former, a laser or electron beam is scanned over a bed of powder; while in the later, powder is blown or wire is fed into the melt pool formed by a laser or electron beam or electric arc or gas arc source. In all cases, parts are typically built up layer-by-layer to form three-dimensional components. See ASTM F2792-12a F42 Committee, “Standard Terminology for Additive Manufacturing Technologies,” ASTM International, 2012. Current techniques allow for deposition via layer-by-layer or successive laser raster passes (hatch-by-hatch). Layer-by-layer and hatch-by-hatch processes are limited in their ability to deposit overhanging structures, control part microstructure, control part properties, and control surface structure and features.
Deposition of overhanging structures is a critical problem in metals-based additive manufacturing. Currently, directed-energy and powder bed additive manufacturing processes have limited capability to deposit overhangs. One approach for depositing a slightly-overhanging structure, with an overhang angle of about 60 degrees is to partially overlay successive cross sections of a component or utilize greater-than-3-axis stage arrangements to tilt the substrate or deposition head during processing. For example, U.S. Pat. No. 6,811,744 B2 discloses methods and apparatus for deposition of 3D parts though directed material deposition slice-by-slice. It also addresses methods for control of the thermal history and properties of the deposited parts. It also includes representations (FIG. 27, 28, 28a, 29) for deposition of overhanging structures. Several preferred methods for production of overhanging structures are addressed. One method allows the motion of a focused laser beam an off-set distance (Δx) (typically less than ½ of the beam spot size) away from the edge of a previously-deposited layer prior to deposition. Next, a contour is deposited along the off-set distance, creating a “slight overhang”. It is claimed that repetition of the process multiple times on a single layer can result in an overhang angle of approximately 60 degrees.
The '744 patent describes the overhang angle as the angle defined by the horizontal (x) axis and the vector connecting the edge of the current and previously deposited layers. After deposition of the overhang, additional depositions beads (line segments) are used to fill in a complete layer. The use of multi-axis stages to reorient the part with respect to the deposition beam is also provided.
US Patent Publication No. 20060003095A1 is a continuation-in-part of U.S. Pat. No. 6,811,744 B2 and discloses that the laser beam off-set distance (Δx) be kept small with respect to the bead diameter. It also discloses methods for the use of specially-configured powder nozzles and multi-axis stages to reorient the part with respect to the deposition beam. The method is preferably implemented by sequential deposition of part cross-sections, layer-by-layer, and allows for the deposition of support structures using lower laser power than the component material followed by removal of the support structure though mechanical means.
Several other approaches for deposition of overhang angles are known. For example, U.S. Pat. No. 5,038,014 describes a method for the formation of components by successive deposition of cross-sectional layers. Each layer includes a number of beads—deposition line segments—spaced and orientation with respect to beads on a previous layer. It is stated that the formation of overhangs requires that a layer must at least partially overlap its underlying layer. However, no further disclosure is provided for the deposition of overhangs.
U.S. Pat. No. 6,410,105 B1 discloses a method for deposition of overhangs, based on deposition of a sacrificial material. The processes requires that the sacrificial material be of a lower melting point than the component material and requires removal of the sacrificial material though melting in a high-temperature furnace.
Additional patents related to voxel printing include U.S. Pat. No. 7,597,420 B2, U.S. Pat. No. 7,206,654 B2, U.S. Pat. No. 6,814,823 B1, U.S. Pat. No. 5,594,652 A. U.S. Pat. No. 7,597,420 B2 and U.S. Pat. No. 7,206,654 B2 relate to multiple, preferably Micro Electro Mechanical, print heads and do not relate to DED or PBF processes or the generation of overhangs. U.S. Pat. No. 6,814,823 B1 relates to a method for ultrasonic welding, with electrical resistance and frictional methods as alternatives, for 3D object fabrication and does not relate to DED or PBF processes or the generation of overhangs. U.S. Pat. No. 5,594,652 relates to a method for dispensing a layer of liquid material onto a platform and does not relate to DED or PBF processes or the generation of overhangs.
A need still exists for methods and systems that can manufacture overhangs, particularly steep overhangs, i.e., overhangs having an angle of or less than 30 degrees, and without the need for specially-designed nozzles or tilt-table arrangements.